1. Field of the Invention
The present invention relates broadly to apparatus and methods of rinsing and drying silicon wafers or other wafers or thin disc-like substrates or elements in the semiconductor process industry. Further, the invention relates to integrated apparatus and methods of cleaning, rinsing and drying wafers, and in particular, to such apparatus and methods for cleaning, rinsing and drying wafers using sonic cleaning techniques.
2. State of the Art
In the processing of silicon wafers to make semiconductor devices, the wafers are subjected to a myriad of processing steps. It is practical to perform many of these steps on a batch of wafers positioned in a slotted carrier which is often referred to as a boat or as a cassette. The carriers have a plurality of spaced slots on the opposite vertical sides thereof for receiving the wafers in edgewise, coaxial, spaced relation. The carriers have openings in the bottom thereof for access to the bottom side edges of the wafers carried thereby. The top of the carriers are open to allow wafers to be inserted and removed therefrom.
Numerous cleaning, coating and diffusion steps are required in manufacturing semiconductor devices. Cleaning and removal of minute particles of dirt and residue from the surfaces of the wafers is a difficult operation. Most small particles of dust, dirt and grime are held rather firmly on the surfaces of the wafers. A vigorous cleaning action is required to remove such foreign matter from the wafers. Manual scrubbing of the wafers, while effective, is costly and destructive due to abrasion.
Immersion of the wafers in hot, chemical solutions has been found to be somewhat effective and is much more cost effective and amenable to mass production than manual scrubbing. To improve upon the effectiveness of the chemical immersion, it has been suggested to use ultrasonic and megasonic cleaning methods either concurrently with or as an adjunct to immersion in the chemical cleaning solutions. Heretofore, such chemical cleaning and sonic energy cleaning methods have been performed in specially adapted cleaning tanks, with the cleaned wafers then being removed from the cleaning tanks to be rinsed in a liquid rinse.
The industry has been using what is known as a spin rinser/dryer for many years to effect a final spray rinse and spin dry of the silicon wafers. The rinser/dryers are essentially centrifuges which throw water from the wafers and the carriers in which the wafers are contained. Because of the spinning action that occurs in these machines, the silicon wafers are subjected to high stress. In addition, silicon dust is generated and redeposited on the wafer surfaces along with other particulate accumulations. The semiconductor industry is moving toward much smaller device geometries in very large scale integration of making silicon devices, and the particulate accumulation on the smaller device geometries creates tremendous defect problems during the final rinse and dry of the wafers.
In my co-pending patent application, Ser. No. 06/874,383 now U.S. Pat. No. 4,722,752 filed Jun. 16, 1986, the entire contents of which are incorporated herein by reference, there is disclosed a method of rinsing and drying thin wafers such as silicon wafers, wherein the wafers are rinsed in a hot water bath while supported in a conventional slotted carrier. The wafers are dried by slowly raising the wafers out of the water bath such that the water surface tension at the surface of the water bath evenly and effectively draws water from the rising surfaces of the wafers. The wafers slowly rise out of the water bath in a dry state without being subjected to the high stress such as developed in the centrifuge type rinsers and dryers.
3. Objectives
A principal objective of the invention is to provide a novel, practical, integrated system for efficiently and simultaneously cleaning, rinsing and drying thin wafers such as silicon wafers which avoids the use of separate and distinct apparatus and methods for the cleaning, rinsing and drying steps.
A particular objective of the present invention is to provide compact, relatively inexpensive apparatus for cleaning, rinsing and drying thin wafers such as silicon wafers in an integrated procedure wherein the wafers are cleaned and rinsed in a tank of high purity, hot, deionized water, with the wafers being slowly passed through a sonic energy field in which they are subjected to sonic wave energy, and then, in a continuation of the slow movement through the energy field, the wafers are dried by slowly removing the wafers from the hot, deionized water in the tank.
A further objective of the present invention is to provide an integrated system in which the wafers are cleaned and rinsed in a tank using laminar, upward flow of high purity, hot, deionized water from the bottom of the tank, wherein the tank is provided with perimeter skimming or overflow to provide efficient removal of particulate contaminants.
An additional objective of the present invention is to provide a novel combination of apparatus comprising a lift mechanism and a cleaning, rinsing tank wherein the thin wafers are lifted from a support cassette while submerged in the hot, high purity, deionized water to first move through a sonic energy field in which the wafers are subjected to megasonic wave energy, and then to continue to move in a slow, continuous motion through the surface of the hot, deionized water to dry the wafers.